Operation Hump was a search and destroy operation initiated by United States and Australian forces on 5 November 1965, during the Vietnam War. The US-Australian objective was to drive out Viet Cong (VC) unit who had taken up positions on several key hills in War Zone D in an area about north of Bien Hoa. The U.S. 1st Battalion, 503rd Infantry Regiment (1/503rd), 173rd Airborne Brigade conducted a helicopter assault on an LZ northwest of the Dong Nai River and Song Be River. The 1st Battalion, Royal Australian Regiment (1RAR) was deployed south of the Dong Nai. On 8 November the major engagement of the operation took place when a VC Regiment attempted to encircle and overrun the 1/503rd resulting in 49 U.S. killed and between 400 and 700 VC killed. On the same day in an engagement known later as the Battle of Gang Toi, 1RAR attacked a VC bunker and trench system, killing six VC and capturing five, while losing two missing. Prelude On 5 November the 173rd Airborne Brigade received intelligence indicating that a VC regimental headquarters, mistakenly reported as belonging to the 272nd instead of the 271st, its three battalions, and the 274th Regiment's D800 Battalion were massed near the confluence of the Dong Nai and Song Be rivers in War Zone D. About twenty-two kilometers northeast of Bien Hoa Air Base, the area had been entered by the Americans several times before. The brigade commander Brigadier General Ellis W. Williamson, organized a force of three battalions: the 1st Battalion, 503rd Infantry, commanded by Lieutenant Colonel John E. Tyler; the 1st Battalion, Royal Australian Regiment, led by Lieutenant colonel Lou Brumfield; and the 3rd Battalion, 319th Artillery Regiment, under Lieutenant Colonel Lee E. Smut. The brigade's third maneuver element, the 2nd Battalion, 503d Infantry, commanded by Lieutenant Colonel George E. Dexter, remained in reserve at Bien Hoa. The plan required the artillery to establish a firebase near the area of operation. Once the firebase was in place, Williamson's infantry would helicopter into the countryside to see what it could find. The only requirement was that the maneuver elements remain within range of the firebase's guns. Operation Early on the morning of 5 November the artillery battalion, accompanied by Troop E, 17th Cavalry Regiment, and Company D, 16th Armor, went into Position Ace (), east of the Dong Nai and about 8 km southwest of its junction